Microelectronics is undergoing a strong diversification in components often intended to be used in more complex devices. Some of these components involve a deformation of a mobile portion under the control of an electric signal in order to form an actuator. In certain cases, a deformation sensor is present therein in order to evaluate the level of deformation obtained by the electric control, advantageously in real time. This evaluation can allow for a retrocontrol of the control of the actuator, for example in order to finely reach a desired level of deformation.
There are techniques, described in publication EP2309559 A1, in order to incorporate a gage for measuring the deformation in an actuator. The structure that is presented therein, in particular in FIG. 1, combines a piezoelectric actuator with a piezoresistive gage connected to a device for measuring resistance. Under the effect of a voltage applied to the terminals of the piezoelectric layer, the structure bends as such deforming the piezoresistive gage. The resistance of the gage is then modified, which makes it possible to evaluate the deformation of the structure. This device however has several disadvantages:                the piezoresistive detection results in a dissipation of energy by the Joule effect, inducing on the one hand an overconsumption of energy and on the other had a heating of the device that can modify the piezoelectric properties of the layer and even degrade the structure.        In case of an external disturbance (for example a variation in temperature), the sensor and the actuator are not affected in the same way, which will induce a measurement error.        In addition, the sensitivity of the sensor decreases when the width of the gage increases, which imposes producing thin gages and therefore more difficult to produce (in thin layers, these limitations can be due to the lithography resolution).        
Publication KOBAYASHI et al entitled “Development of Self-sensitive Piezoelectric Cantilever Utilizing PZT Thin Film Deposited on SOI Wafer” from INTEGRATED FERROELECTRICS, Vol. 89, 2007, pages 116-122, discloses an actuator that comprises a stack with two electrodes and an inserted piezoelectric layer. It also comprises a deformation sensor with a sensor electrode that measures a signal of the voltage at this level, in relation with the frequency of the input signal of the actuator. This voltage signal frequency information is then used. Even if the measuring electrode is individualized and separated from the one used for actuating, this here is a measurement of the voltage coming from a vibration and piezoelectric behavior of a stack of layers.
An equivalent technique is presented in publication WATATSUKI N et al entitled “Piezoelectric Actuator of LiNbO3 with an Integrated Displacement Sensor” from JAPANESE JOURNAL OF APPLIED PHYSICS, Vol. 37, no. 5B, 1998, page 2970-2973.
Disadvantages in frequency detection with current techniques are:                that the measurements are difficult (as the instrumentation is complex), not very accurate; there are issues with absorption linked to the atmosphere that can introduce measurement uncertainty. Moreover an actuator does not need in general to be actuated at its resonance frequency for its mobility as such, but this is what is imposed by the frequency detection method and which can in particular accelerate the aging of the component.        that the most effective actuator materials such as PZT are often poor resonators and reciprocally (a good resonator and not as good actuator), which requires choices that penalize either mobility, or the measurement.        
It is therefore an object of the invention to overcome at least partially the disadvantages of the current techniques by offering an actuator in which a deformation measurement can be taken in an improved manner.